The 1960s archived image data (film strip) from the
Nimbus program has apparently now all been digitised and looks like it is being or has been placed in the public domain. It is a treasure-trove of historic meteorological data that we had been unable to easily access in any scientifically useful way until now, and it has already yielded surprising results that pose new questions about how the Earth's weather systems tick.
There are notes and a link to a very interesting 6-minute video here:
1960’s satellite imagery of polar ice discovers “enormous holes” in the sea ice 
